Urea-aldehyde sealing agents and method of making the same



Patented July 31, 195i UNITED 2,562,863 ICE UREA-ALDEHYDE SEALING AGENTSAND METHOD OF MAKING THE SAME Stewart S. Kurtz, Jr., Mei-ion, and JamesS. Sweely, Swarthmore, Pa., assignors to Sun Oil Company, Philadelphia,Pa., a corporation of New Jersey No Drawing. Application October 14,1948, Serial No. 54,587

This invention relates to a sealing agent and the preparation thereofand more particularly to an improved sealing composition adapted forplugging porous subterranean formations.

The novel sealing agent of the present inven tion comprises an'aqueoussuspension of a thermosetting resin prepared by causing urea andformalin or urea and furfural to react to a particular stage ofcondensation, as hereinafter fully described, and capable of furthercondensation to a hard infusible stage.

In'the drilling of Wells for oil, gas or other fluids the well boretraverses numerous formations or strata of varied porosity, such ascavernous limestone, gravel beds, oil-bearing sands, cavernoussandstones, water-bearing sands, gasbearing sands and the like, it isfrequently necessary or desirable for one reason or another to seal offcertain of these formations from the borehole and many methods foreffecting such sealing have been proposed. In drilling by the rotarymethod a drilling mud'is circulated during the general drillingoperation down through the drill pipe to the drill bit and thence backto the surface to overcome the formation pressure, lubricate the bit,carry cuttings to the surface and to wall off the borehole. It is notinfrequent, however, that formations are encountered which aresufficiently porous that the mud fluid passes into the formation so thatlittle or no mud returns to the surface. This condition, which is knownas lost circulation, may also be due to a breakdown of one or more ofthe formations traversed, caused by the high hydrostatic pressureexerted by the mud column on the formation as when the mud fluid hasbeen heavily weighted with weighting material. In such cases steps mustbe taken to seal off the porous formation and prevent the loss of mudfluid. Again, it is often'desirable to plug off certain strata in orderto prevent-or 6 Claims. (Cl. 26029.4)

minimize ingress of undesirable fluids into the well. For instance, itmay be desired to seal off Water-bearing sands to increase the ratio of'oil to water production.

Formerly it was general practice to accomplish such sealing operationsby pumping cement grout into the well, forcing it into the porousformation, permitting it to harden in place and then drilling throughthe cement remaining in the borehole. Although in the case of lostcirculation it has become customary more recently to add special sealingagents such as ground sugar cane stalks, mica or cellophane to thedrilling fluid to improve its sealing properties, this has often provedunsuccessful, and consequently cementing operations are still used to anextent to be allowed to set within the borehole in order to insuresealing of the porous formation. It frequently happens that in drillingthrough the hardened cement the hole becomes sidetracked into theadjacent formations, thus requiring redrilling of all the hole below thepoint of sidetracking, perhaps including the zone of lost circulation.Similar disadvantages accompany the use of cement in sealing off watersands. A further disadvantage may arise due to the possibility that, insome cases, the cement may be forced into the oil-bearing formation to adistance Sllfficient to make it diflicult or impossible subsequently toopen the formation for production by the usual gun perforation methods.

More recently the use of resin-forming liquids capable of condensing toa solid resin under the influence of the formation temperature in placeof cement has become known and has attained a limited applicabilityparticularly in sealing water-bearing sands. While such resin-formingliquids offer certain advantages over cement, such as greater fluidityresulting in improved sealing properties and better resistance tonatural brines and to acid such as used in acidizing wells, they fail toovercome the above discussed disadvantages which accompany the use ofcement. Like cement, these resin-forming liquids solidify in theborehole, necessitating redrilling of that portion of the hole whichthereby becomes plugged. Also, due to the greater fluidity of theresinforming liquids as compared to cement grout, they are even more aptto penetrate an oil-bearing stratum to such extent thatsubsequent-opening of the stratum for production becomes impossible. Afurther disadvantage of this type of sealing agent arises when there aresubstantial variations in penetrability of the earth surrounding theportion of the boreholeto be sealedoif, as occurs in the case of ahighly porous formation adjacent to a less porous formation or as-may becaused by crevices within a formation. In such cases a very large amountof the resin-forming liquid may be forced into the more penetrableportions of the surrounding earth before an effective seal of the lesspenetrable portions is obtained, with the result that the expenseinvolved in carrying out the sealing operation becomes excessive.

The present invention is directed to and provides an improved sealingagent which overcomes the above-discussed disadvantages of sealingagents heretofore employed. The novel sealing composition according tothis invention comprises a suspension in water of a thermosetting resinprepared by reacting urea and formalin or urea and furfural undercondensation conditions, the resin being partially condensed to aparticular intermediate stage requisite to impart to the suspensionthedesired sealing characteristics. This particular stage of condensationmay be described as an intermediate plastic solid stage. The partiallycondensed resin corresponding thereto is dispersible in water, byconventional mechanical means and without the aid of an emulsifyingagent, to a state which is substantially non-coalescing for at leastfive hours, i. e. the dispersed resin particles do not coalescesubstantially when the suspension is permitted to stand for this periodof time. The suspension obtained by dispersing in water the resincorresponding to the aforesaid particular intermediate plastic solidstage, which suspension constitutes the sealing agent of the presentinvention, is characterized by its ability, when forced into a bed ofgranular material such as sand or gravel having void spacessubstantially larger than the size of the dispersed resin particles, toform a resin plug at the face of the bed, which, upon application ofheat, will condense to a hard layer substantially impervious to drillingfluids. In other words, the suspension is capable of forming a resinplug or sheath at the face of a porous body without any considerablepenetration of the resin into the body even though the latter has poresor voids which are substantially larger than the dispersed resinparticles. Further, this resin plug under the influence of heat willcondense to a hard sheath impervious to drilling fluids and havingconsiderable mechanical strength as distinguished from a crumbly orpowdery resin layer.

The aqueous suspensions of the present invention have the greatadvantage over previously known sealing agents of not forming adifiicultly drillable solid mass within the well bore. While the resinparticles of the suspension which remains in the borehole may coalesceto an extent with time, the coalesced resin upon curing under boreholeconditions does not become the hard solid mass that is obtained when aresin-forming liquid or cement grout is used as the sealing agent.Furthermore, after the resin layer has been plastered out on theborehole wall, setting of unplastered resin to a solid mass within theborehole may be minimized or prevented by flushing out the suspensionbefore the resin has had time to cure. This may be accomplished bycirculating a stream of water into and out of the borehole, preferablyslowly to insure against the possibility of flushing out part of theplastered resin layer. The resin layer remaining on the borehole walland slightly penetrating the adjacent formation cures under theformation temperature to a hard sheath which generally may be of theorder of one-quarter to one inch thickness. Thus, any oil-bearingstratum which has been sealed off may readily be opened up forproduction by the usual gun perforation method. A further advantageresults from the ability of the suspension to plaster out at the face ofeven a very porous formation, such as one-quarter inch gravel, sincethis characteristic prevents deep penetration of the resin into theformation and thus reduces to a minimum the amount of resin required toobtain an effective seal. Also the fact that the sealing agent whichremains in the borehole is composed partly of water instead of entirelyof resin further reduces the amount of resin required for carrying outthe operation.

The first step in the procedure of preparing the sealing agent of thisinvention comprises reacting urea and formalin (which consists of about40% formaldehyde in aqueous solution) or urea and furfural undercondensation conditions to the desired stage. An acid or alkalinecatalyst 4 may be used to change the speed of the reaction.

In the case of the urea-formaldehyde type resin, satisfactory sealingagents can be prepared within reasonable periods of reaction time whenfrom 1 to 2 parts of formalin per part of urea by weight are used. When1 /2 parts of formalin per part of urea are used, the presence of sodiumhydroxide acts to decrease the speed of the reaction, whereas thepresence of hydrochloric acid acts to increase the speed of reaction.Since, at this ratio, the reaction time without catalyst is quite short,the use of caustic soda to decrease the reaction rate at such a ratiomay be advantageous in that it will facilitate the stopping of thecondensation at the desired stage. The product, however, may be inferiorto that obtained without a catalyst.

When the reactants are initially mixed, they form a White slurry. Twophases are present, solid urea and aqueous formaldehyde. The mixture isthen brought'to the reaction temperature, which is preferably between C.and C. During this increase in temperature or shortly thereafter, themixture clears, becoming a single phase solution having the appearanceof water.

Upon further reaction, the liquid becomes more viscous until a point isreached at which a second phase precipitates from the reaction mixture.This phase is the partially condensed urea-formaldehyde resin. Thereaction mixture assumes a milky appearance, becoming denser and moreopaque as the precipitated resin increases in quantity until a point isreached at which the stirring is no longer capable of keeping thereaction mixture relatively homogeneous and the resin phase becomes adistinguishable white mass, a soft, pasty semi-liquid material.

As the reaction proceeds still further, the resin mass gradually changesin appearance and properties, passing through a stage at which it isgummy and resembles a solid more than a liquid. Finally, the resin phaseenters the stage wherein it is a plastic material, of properties thatwill be different according to the original reactant proportions and tothe catalysis conditions prevailing in the reaction. It may be either awhite, plastic solid or a White mass with the appearance and consistencyof set gelatin, but in either case, in this stage, it is recognizablydiiferent from the resin phases of the earlier stages.

The above description of the behavior of the reaction mixture refers tothe conditions prevailing at the reaction temperature, which ispreferably an elevated temperature of about 90 C.-100 C. The conditions,however, at which the suitability of the resin product for use in thepresent invention are determined are those prevailing at ordinarytemperatures of about 20 C.-30 C. In order to determine the roomtemperature properties of a resin phase produced after a given period ofreaction time has elapsed, the resin phase may be separated from therest of the reaction mixture and mixed with cold water to reduce itstemperature quickly and t prevent any further reaction beyond the timeat which it is desired to know the room temperature properties of theresin product.

When the above procedure is carried out, it is discovered that the resinphase at room temperature may have a different appearance than at thereaction temperature. For example, a reaction mixture that is still apasty semi-liquid at the reaction temperature may, at certain reactantratios and under certain catalysis conditions, become a heterogeneoussystem upon cooling with .at all.

amass? If the reaction is stopped before the intermediate plastic solidstage is reached, the result will be a product which will beunsatisfactory for use in the present invention. Such products includeproducts which are, when cool, liquids or sticky semi-liquids or gummysemi-solids. which is liquid when cool may be suspendible in water withthe aid of an emulsifying agent, but the suspension will not plaster oncoarse sand, but instead penetrate deeply into formations of semi-liquidtype when cool cannot be suspended A product of the gummy,'semi-solidtype may be difficultly suspendible, but the suspension will tend tocoalesce within a short time, that is within five hours.

While reaction temperatures of 90 C.-100 C. have been described asoptimum, it is to be noted that higher and lower temperatures may beused with satisfactory results in both the formalin and furfuralreactions.

In the case of the urea-furfural type resin, satisfactory sealing agentscan be prepared within reasonable reaction times when from one to sixparts of furfural per part of urea by weight are used.

When the reactants are initially mixed, they form a black mixture inwhich two phases are present, solid urea and liquid furfural. Theinitial appearance of this mixture, when agitated, differs according tothe relative proportions of reactants used. When urea predominates, themixture has the appearance of a black slurry. Mixtures with increasingproportions of furfural tend more to the appearance of a liquid than aslurry. At high ratios of furfural to urea, the

initial mixture appears under agitation to be a viscous liquid; solidconstituents are not readily discernible.

After the reactants are mixed, they are brought to the reactiontemperature, which is preferably between 90 (L-100 C. During thisheating, the agitated mixture becomes more homogeneous in appearance,tending more toward liquid, rather than slurry, nature. As the reactionproceeds, however, partially condensed resin begins to form, whereuponthe mixture will begin to become more viscous again, and the solidconstituents will become more readily distinguishable, so that themixture itself begins to behave less like a liquid 1. A product anysubstantial porosity. A product of the sticky,

and more like a solid under the agitation. The

wherein the partially condensed resin predominates to such an extent andis itself of a sufficiently advanced degree of condensation that thereaction mixture is composed of a black plastic solid admixed with justenough liquid to render it capable of being stirred.

The stage just described is the desired intermediate plastic solid stageat which the resin is suspendible in water by stirring and thesuspension is capable of persisting for a substantial period of time,such as at least five hours. The reaction should be stopped during thisstage. If it were stopped earlier and an attempt made to suspend theproduct without the aid of an emulsifying agent, either the productwould not suspend or it would form a suspension incapable of persistingfor five hours.

It is to be noted that the above described behavior of the reactionmixture will vary somewhat according to the initial reactantproportions, but in any case, the desired product is that obtainedwithin the intermediat plastic solid range, and a few trial runs willenable a skilled operator to recognize from the appearance of thereaction mixture the proper stopping point for any given ratio withinthe operable range.

If, with either type of resin, the reaction is allowed to proceed toofar, the resin will become too tough or hard for the suspendedparticles, upon plastering and curing on sand or gravel, to fusetogether properly and thereby produce a resin layer having goodmechanical strength. More orless concurrently, although not exactly so,the resin will tend to lose its ability to be dispersed in theconventional manner or at least will be dispersible only with greatdiiiiculty. The first indication, however, that the reaction is beingcarried past the desired stage is shownby the nature of the resin layerobtained on forcing an aqueous suspension of the resin product into abody of sand or gravel. Although the resin may still be suspendible andmay plaster out from the suspension at the face of the porous material,the resulting resin layer after curing under the influence of heat willtend to have poorer mechanical strength, being hard but brittle if thereaction has proceeded somewhat further than is desirable and thenbecoming crumbly or powdery if the reaction has proceeded substantiallypast the desired stage.

The range in degree of condensation between a product which is too softand one which is too hard to produce a suitable sealing agent is ratherlimited. It is important that the reaction be stopped within this rangeand preferably well within the range for this gives a product which isreadily dispersible to a non-coalescing state, which will plaster outof'the suspension properly yielding a resin layer which on curingbecomes a strong sheath, and which, in addition, can withstand areasonable amount of preheating of the suspension without substantialloss of plastering and curing qualities. This last-named property ofretaining the desired sealing characteristics even after the suspensionhas been heated for a reasonable time (e. g., one hour at F. or onehalfhour at 200 F.) serves, in practice to insure effective sealing of theformation even when there is a substantial interval between the time ofintroducing the suspension into the borehole and the time it reaches,and the resin plasters out on, the formation.

The final step in the preparation of the sealing agent comprises formingthe resin-in-water suspension. This may be carried out simply byvigorously mixing together the resin and water as by means of amotor-driven stirrer. In cases where a catalyst has been used to promotethe condensation reaction, the catalyst may at this point be washed outof the partially condensed resin by first agitating the latter withseveral volumes of water until it is well dispersed, al-

lowing the mixture to stand for a short time sufli- A series of runs wasmade in which for each of a number of varying ratios of urea to formalinthe time required to form a product satisfactory for making the sealingagent was determined. No catalyst was used, and the temperature wasmaintained between 90 C.-100 C. With urea to formalin ratios between 2to 3 and 2 to 5, products corresponding to the desired stageofcondensation were obtained. At ratios beyond these limits, productscould not be formed which would give suspensions capable of plasteringon 10 mesh sand. At ratios within the limits, products satisfactory forforming the sealing agent were obtained at the following reaction times:

Urca- Reaction formalin time,

ratio minutes Example I I A series of runs was made in whichurea-formaldehyde resins were prepared, with reaction times varying ineach run. In each run, 100 parts of urea and 260 parts of formalin weremixed, and the mixture was heated to a temperature of approximately 94"C. and reacted without catalysis at this temperature. During thereaction the mixture was constantly stirred by means of a motor-drivenstirrer and the temperature was maintained near 9l C. by means of aconstant temperature bath surrounding the vessel. After the reaction hadbeen stopped, the resin was separated from the rest of the reactionmixture and the separated resin was tested for dispersibility andsealing qualities. The ability to form a noncoalescing suspension wasdetermined by mixing with water in themanner described hereinbefore. Thesealing qualities were determined by forcing the resulting suspensioninto a bed of 10 mesh sand, then curing the resin filter cake at atemperature of 200 F. and observing the character of the cured cake. Thefollowing results were obtained:

Reaction time= minutes. The product was a thick white paste at thereaction temperature and a soft, white semi-solid when cooled by contactwith water. The resin formed a coarse suspension with water, whichplastered on 20-30 mesh sand and cured in 4 hours to give a brittlefilter cake.

Reaction time=l0 minutes. The product was a thick white paste at thereaction temperature and a soft, white semi-solid at room temperature.The resin formed a coarse suspension with water, which plastered on meshsand and cured in 3 /2 hours to give a hard filter cake which fracturedeasily.

Reaction time=16 minutes. The product was a thick white paste at thereaction temperature and a soft, white semi-solid at room temperature.The resin formed a coarse suspension with water, which plastered on 10mesh sand and cured in 6 hours to give a hard filter cake whichfractured easily.

Reaction time=5fl minutes. The product was a thick paste at the reactiontemperature and a thick, gummy semi-solid at room temperature. The resinformed a coarse suspension with water, which plastered on 10 mesh sandand cured in 2 hours to give a very brittle filter cake.

Reaction time=l00 minutes. The product was a thick pasty material whenhot and a gelatinous material when at room temperature. The resinsuspended in water and plastered on 10 mesh sand, giving a satisfactoryfilter cake in 2 hours.

Reaction time=l25 minutes. The product and resin obtained were similarto those obtained at 100 minutes. A satisfactory filter cake Was formedin 3 hours on 10 mesh sand.

Reaction time=200 minutes. The product and resin obtained were similarto those obtained at 100 and 125 minutes. A satisfactory cake was formedin 2 hours on 10 mesh sand.

Reaction time=3013 minutes. The product was a thick slurry when hot anda hard White solid when cold. The resin suspended in water and gave abrittle filter cake on 10 mesh sand in 2%.; hours.

Reaction time=392 minutes. The product was a soft solid when hot andhardened considerably on cooling. The resin formed a suspension withwater which showed a slight tendency to coalesce. The suspensionplastered on 10 mesh sand, but would not soften sufficiently to form asatisfactory filter cake. This indicated that longer reaction timeswould not give products suitable for use in the present invention.

Example III Runs were made at urea to formalin ratios of 2 to 3 with twodifferent catalysts. The average temperature of reaction was in bothcases 97 C.

With 1% of caustic soda in the reaction mixture, a product was obtainedin 378 minutes that was satisfactory, though inferior in plasteringqualities to the product obtained without a catalyst.

With 1% of concentrated hydrochloric acid in the reaction mixture, asatisfactory product was obtained in 5 minutes.

Since the required time in the uncatalyzed case of Example I was 10minutes, it appears that at a 2 to .3 ratio, caustic soda greatlyincreases the time of reaction, while hydrochloric acid decreases it.

Example IV A series of runs was made in which for each of a number ofvarying ratios of urea to furfural, the time required to form a productsatisfactory for making the sealing agent was determined. No catalystwas used, and the temperature was maintained between C. and 100 C. Withurea to furfural ratios between 1 to 1 and 1 to 6, productscorresponding to the desired stage of condensation were obtained. Athigher ratios, the relative amount of solid in the reaction mixture wasso great that the latter could not be stirred and conduction of thereaction under such conditions was impracticable. At lower ratios,products could not be formed which would give suspensions capable ofplastering on 10 mesh sand. At ratios within the limits, productssatisfactory for forming the sealing agent were obtained at thefollowing reaction times:

Urea- Reaction furfural time,

ratio minutes ill 45 l/2 45 1/6 65 In sealing a formation by introducingthe sealing agent into the borehole and forcing it into the formation,either the concentrated suspen sion or a dilute suspension of the resinmay be used. It has been found that contamination of the sealing agentby minor amounts of drilling mud, such as may happen during actual useof the sealing agent in a well bore, does not cause any decrease in theplastering ability of the suspension nor does it cause any substantialloss in mechanical strength of the cured resin layer. However, drillingmud in amount over 50% in the suspension results in a resin layer havingpoorer mechanical strength and generally unsatisfactory for eifecting agood seal.

We are aware that it has been proposed heretofore to incorporate athermosetting resin or reactants capable of forming such resin in thedrilling fluid circulated during the general drilling operation. Thesealing agent herein described, however, is not a drilling fluid and isnot suitable for use during the general drilling operation.

This application is a continuation-in-part of an application filedAugust 9, 1945, Serial No. 609,927, now U. S. Patent 2,457,160 issuedDecember 28, 1948.

In our copending applications Serial Nos. 54,586 and 54,588 both filedOctober 14, 1948, of which 54,588 has matured into Patent 2,559,162issued July 3, 1951, there are disclosed and claimed the methods ofpreparing sealing agents by condensing melamine or thiourea in certainproportions with formalin or furfural to an intermediate plastic solidstage at which the resin formed exhibits certain properties, stoppingthe reaction at that stage and dispersing the resin in water to form anon-colloidal aqueous suspension. The method of sealing a porousformation traversed by a borehole by means of the sealing agent of thepresent invention is not herein claimed as that forms the subject matterof our copending application Serial No. 609,928 filed August 9, 1945.

We claim:

1. Method of preparing a sealing agent for sealing porous formationswhich comprises reacting urea with a reactant selected from the groupconsisting of formalin and furfural under condensation conditions toform a thermosetting resin, the weight proportion of urea to thesecond-named reactant being within the range of one to 1 2 when saidsecond-named reactant is formalin and one to 1-6 when said secondnamedreactant is furfural; continuing the reaction until the resin hasreached an intermediate plastic solid stage at which it is, when saidsecond-named reactant is formalin, a distinguishable mass in thereaction mixture and is disp-ersible by stirring in water without theaid of an emulsifying agent to form a non-colloidal suspension stablefor at least five hours; stopping the reaction when said intermediateplastic solid stage is reached whereby to obtain a partially condensedresin capable of further condensation to a hard infusible stage uponapplication of heat; and dispersing the resin in water thereby forming,as the desired product, a non-colloidal aqueous suspension which, whenforced into a bed of 10 mesh sand, will form a resin sheath at the faceof the bed capable of thermosetting to a hard layer non-porous todrilling fluid.

2. A sealing agent prepared in accordance with the method defined inclaim 1.

3. Method of preparing a sealing agent for sealing porous formationswhich comprises reacting urea with formalin in the weight proportion ofone part of urea to 1 /2-2 /2 parts of formalin under condensationconditions to form a thermosetting resin; continuing the reaction beyondthe stage at which the reaction mixture appears milky and until theresin has reached an intermediate plastic solid stage at which it is adistinguishable mass in the reaction mixture and is dispersible bystirring in water without the aid of an emulsifying agent to form anon-colloidal suspension stable for at least five hours; stopping thereaction when said intermediate plastic solid stage is reached wherebyto obtain a partially condensed resin capable of further condensation toa hard infusible stage upon application of heat; and dispersing theresin in water thereby forming, as the desired product, a non-colloidalaqueous suspension which, when forced into a bed of 10 mesh sand, willform a resin sheath at the face of the bed capable of thermosetting to ahard layer non-porous to drilling fluid.

4. A sealing agent prepared in accordance with the method defined inclaim 3.

5. Method of preparing a sealing agent for sealing porous formationswhich comprises reacting urea with furfural in the weight proportion ofone part of urea to 1-6 parts of furfural under condensation conditionsto form a thermosetting resin; continuing the reaction until the resinhas reached an intermediate plastic solid stage at which it isdispersible by stirring in water without the aid of an emulsifying agentto form a non-colloidal suspension stable for at least five hours;stopping the reaction when said intermediate plastic solid stage isreached whereby to obtain a partially condensed resin capable of furthercondensation to a hard infusible stage upon application of heat; anddispersing the resin in water thereby forming, as the desired product, anon-colloidal aqueous suspension which, when forced into a bed of 10mesh sand, will form a resin sheath at the face of the bed capable ofthermosetting to a hard layer nonporous to drilling fluid.

6. A sealing agent prepared in accordance with the method defined inclaim 5.

STEWART S. KURTZ, JR. JAMES S. SWEELY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,899,109 Ripper Feb. 28, 19332,197,724 Hovey et al. Apr. 16, 1940 2,249,795 Theis July 22, 19412,294,873 DAlelio Sept. 1, 1942 2,345,611 Lerch et al Apr. 4, 19442,456,191 Hewett Dec. 14, 1948

1. METHOD OF PREPARING A SEALING AGENT FOR SEALING POROUS FORMATIONSWHICH COMPRISES REACTING UREA WITH A REACTANT SELECTED FROM THE GROUPCONSISTING OF FORMALIN AND FURFURAL UNDER CONDENSATION CONDITIONS TOFORM A THERMOSETTING RESIN, THE WEIGHT PROPORTION OF URA TO THESECOND-NAMED REACTANT BEING WITHIN THE RANGE OF ONE OT 1 1/2-2 1/2 WHENSAID SECOND-NAMED REACTANT IS FORMALIN AND ONE TO 1-6 WHEN SAIDSECONDNAMED REACTANT ID FURFURAL; CONTINUING THE REACTION UNTIL THERESIN HAS REACHED AN INTERMEDIATE PLASTIC SOLID STAGE AT WHICH IT IS,WHEN SAID SECOND-NAMED REACTANT IS FORMALIN, A DISTINGUISHABLE MASS INTHE REACTION MIXTURE AND IS DISPERSIBLE BY STIRRING IN WATER WITHOUT THEAID OF AN EMULSIFYING AGENT TO FORM A NON-COLLOIDAL THE REACTION WHENSAID INTERMEDIATE PLASTIC SOLID SUSPENSION STABLE FOR AT LEST FIVEHOURS; STOPPING THE REACTION WHEN SAID INTERMEDIATE PLASTIC SOLIDCONDENSED RESIN CAPABLE OF FURTHER CONDENSATION TO A HARD INFUSIBLESTAGE UPON APPLICATION OF HEAT; AND DISPERSING THE RESIN IN WATERTHEREBY FORMING, AS THE DESIRED PRODUCT, A NON-COLLOIDAL AQUEOUSSUSPENSION WHICH, WHEN FORCED INTO A BED OF 10 MESH SAND, WILL FORM ARESIN SHEATH AT THE FACE OF THE BED CAPABLE OF THERMOSETTING TO A HARDLAYER NON-POROUS TO DRILLING FLUID.